No. The normal definition of casualty is "become unavailable for military duty." This can be due to disease, injury, death, or other factors.

Since WWI is over, there is no need for further military duty to serve in the war, so there are no further casualties of WWI. By the definition of "casualty", nobody who died after 1918 can be considered a "casualty of war".

But I think you are really asking about a vaguer topic, such as "victims of war" or "deaths in the war" rather than "casualties". This is much harder to answer, because it is fundamentally a semantics problem. The answer comes down to what do you mean by your question.

We can clearly answer questions like "how many people died from 1914 to 1918?" Obviously, somebody dying in Belgium last week (regardless of the cause) is not included in this group.

It becomes a little bit vague when you start asking "how many people died due to WWI?" It's not clear if Joe had a heart attack because the artillery shell blew up his family or because he's an old man. It doesn't really matter if Joe died in 1917 or 1927, as we can't clearly say that his death due to heart attack was due to the war.

If you define your question differently, such as "how many people died from military action during WWI?", then most people would say "yes, an artillery shell exploding after the war is still the result of military action from WWI".

As another example, Europe had an enormous famine in 1947. Clearly WWII had a major impact, but it was also one of the coldest winters on record. For people that died due to starvation or exposure during this famine, it's impossible to say whether it's due to bad weather or due to the War, or some other cause (such as old age).

This is further complicated by the fact that there were major migrations in the face of the dawning of the Cold War, the advent of Israel, and flight from Europe of many people to the Western Hemisphere. This makes the records of this period very chaotic (for example, many people disappeared from a village, and we don't know if they died or emigrated). War is inherently messy, which makes it difficult to provide clean cut-and-dry answers to any question.

this is a really good question. i wonder if there is precedent for this.

The answer to this question depends on how you want to define the casualties of a war. As petrov pointed out, casualty does not refer to deaths exclusively. I'll use the term to refer to this anyway. In the most simple case, one might define casualties of a war as the sum of those directly killed by actions of participants in a war. On its face, this method works. It considers those killed in battle as well as civilian casualties while excluding most people killed in conflicts entirely unrelated to the war. However, this simple approach has several issues upon deeper inspection. For one, who is a participant in a war? Certainly the governments involved may be considered, but are all prisoners executed by them in the day-to-day functioning of the state also to be considered casualties of a war? Secondly, what about indirect actions? As an example, let us look to the famines in Nazi-occupied Greece. It's recorded that due to Nazi policies, the country was looted of most of its goods and resources in order to feed occupied troops. As Göring rather famously said:

I could not care less when you say that people under your administration are dying of hunger. Let them perish so long as no German starves. This starvation was not the result of direct action, but rather the indirect result of Axis policy. The deaths resulting from this affair are typically counted in WWII casualty figures.

This brings us back to the original question: What do we mean by casualties in a war and how do we estimate them? In order to proceed, we need to understand something about the history of civilian casualty estimates. Thankfully, Seybolt et al did all the hard work for us in Counting Civilian Casualties. While the entire history is too long to present here, at the time of WWII, there was little legal status of civilians as official participants in a war and hence, they were not often considered as the casualties of the war. Largely as a result of atrocities inflicted on civilian populations during WWII, this view was quickly amended in subsequent treaties and conventions.

With this newfound knowledge, we can hopefully amend our previous attempt to more accurately capture what we mean by casualties.

Those killed in a war due to actions or conditions created thereof by participants in the pursuit of war goals.

We're still stuck trying to find that pesky definition of participants in the war, though. As might be expected, this is a topic of some debate and various definitions abound. Academic studies of warfare tend to follow the two major projects, COW and HIIK. Both of these are characterized by a recognition that war is a temporary state of a nation. Accordingly, both projects assign deaths to wars during the period a war is considered to have occurred, by their respective criteria. Under this definition of participants, one might say that the ordnance casualties are part of WWII.

However, if it has not become clear yet, there are many, many methodologies for calculating deaths of war and in some situations, one or another might be more appropriate. The statistics serve both political and historical purposes and different definitions will not necessarily produce the same results. Even under equivalent definitions, war deaths are inherently estimates and compared to the typical error in reported deaths, long-tail deaths from historical actions are often negligible.

Under Belgian law they would be officialy counted as a civil victim of war and have the right to all the benefits befitting a casualty of war. However this only applies to those with Belgian nationality and the victims here weren't (turkish and bulgarian).