No, you're not an asshole, the other person is the asshole by de facto demanding you to do their work (when people get all pissy if you say "no" for something they "asked" you for, they weren't really asking).

If you want to preemptivelly remove or reduce the risk of others accusing you in some way of "meaness" (such "asking" and the "meaness" accusation on refusal being quite a common strategy of people who were far too spoiled as kids and never really grew up - they do it because the "oh, look at poor little me" worked when they were kids to reverse adults' "no" responses), provide some kind of "yes" under conditions and a time frame entirelly defined by you, something like "I would love to help you but I'm really busy at the moment with higher priority work. If I get the time I'll come around and help you with that". From this point either go down the line of "never having the time" (i.e. you don't do it and have no intention of doing it, and if confronted just provide vague "I couldn't get around to doing it" or just "I forgot and now it's too late" reasons that can't really be disproven by the other person) and they'll eventually give up on asking you that (being pissy about people being too busy with more important work doesn't really work as well as being pissy about an outright "no"), or you go down the line of "helping others help themselves" (i.e. you do some of the work as long as they're right there also doing the work with you or take them to the right person to ask for help if there is one and wait with them while they ask and next time around when they come to you, ask them "have you asked person X already").

Personally the way I solved my own "not wanting to be seen as not nice" way back when I started working was a mix of prioritization (i.e. "I'll help you when I have the time", and I genuinelly meant it but in practice I rarelly had the time) and helping people help themselves (i.e. "I'll explain you how you do it while you do it yourself" and afterwards for subsequent requests just asked "have you tried already what I taught you last time?" and not help until they did which usually resulted in them solving the problem themselves) though this was in software development and people came to me to solve the kind of problems that had to do figuring something out, diagnosing a problem or implementing a certain kind of functionality, so I could do the whole "teach them whilst they do it themselves" thing.