Very, very different. To begin with, equipment like hydrometers and thermometers weren't used yet by Central European brewers and yeast monocultures wouldn't be developed until the late 19th century by Carlsberg and Heineken. Centrail European malts were also darker. Pilsner Malt, which is the base of most lagers today, wouldn't be invented until a decade later. Things like sanitation were also not standard yet among brewers.

So, a lager brewer of that time would likely produce a darker beer than your typical lager and will brew it without any kind of temperature control, even during the mashing. Different brewers had different methods to estimate the temperature, which were passed from generation to generation. They also didn't really know how strong the beer was, only an educated guess, at best.

Once the brewing proper was done, the wort was cooled and sent to ferment. The yeast would be sourced from the previous batch and they would basically hope for the best, as they had little, if any control over the fermentation process, and many lagers had a much lower degree of attenuation (how much sugar the yeast convert into alcohol) than modern ones.

Things began to change in the following decade after Sebastian Sedlmayr (owner and brewer of Spaten, in Munich) and Anton Dreher (a brewery owner from Vienna) returned from their joint trip to England, a country whose brewing industry at the time was far more developed than any other. But, at least in Europe, what you would get (provided you could get lager, which wasn't as popular yet) would likely be a darker, thicker and more acidic beverage than today.

Now, what I would like to know is whether Yuengling brewed lagers at the beginning. I somehow doubt it. The founder was from Baden-Württenberg, which is more a wine country, actually.

Here's a similar question with answers, also inspired by Yuengling: https://www.reddit.com/r/AskHistorians/comments/6ro6vd/im_sitting_at_ororkes_bar_in_gettysburg_looking/