A couple assumptions to unpack here.

First, that agricultural societies necessarily have access to more technology. While this may be true to a degree, necessity being the mother of invention is probably even more true. I'm sure someone who knows more about Central Asia than I do can confirm, but I believe there were several technological advancements made in the realm of stirrups and bows that allowed for horseback archery as the primary form of Mongol warfare, all stemming from being a nomadic society centered on the mobility provided by horses.

Secondly, the assumption that greater access to technology (lets say military technology specifically) necessarily equals success in warfare. While certainly an advantage, technology does not solely dictate the ability to conquer or win battles. A technological advantage, just like any advantage, can be squandered and amount to no advantage at all. For extreme examples, see the Battle of Isandlwana and the Battle of Adwa. Alternatively, look at the conquest of central Mexico by Cortez. Whatever technological advantage the Spaniards had was certainly not enough to overcome the huge numerical superiority of the Aztec forces (at least before employing the Tlaxcalans and other native groups to fill out the ranks) or the logistical disadvantage of fighting in hostile terrain far from allied territory.

All that said, I'm not a military historian or a specialist in Central Asian history, so my details and interpretation could be off. I hope someone with more knowledge in these areas can provide more information and correct me where I err.

However, I do think the overall premise of the question is based on some flawed assumptions. Most importantly, the idea that the Mongols couldn't somehow acquire technological advances from other people. Societies and cultures aren't discrete entities bumping up against each other. People interact with each other, often times over quite considerable distances. People are also generally quite keen on copying innovations that they think will be useful to them.

Consider also that not all agricultural societies invent all the technology they use. Agriculture itself was only developed in 7-9 different places on the planet, but was picked up by people outside those locations who didn't develop it themselves. There is no real reason a nomadic group would have more difficulty in adopting innovations from other societies less so than an agricultural group that didn't invent, say, a writing system or ironworking.