Where online was it and did you talk to this person before or was it a random private message.
I mostly ask because yes, it can just be a nice compliment which is great....depending on where it comes from.
I know if your on like the Amino social media app for example and you get a PM from a lv 1 stranger saying that, you block them right away, it's EXTREMELY likely they are a ->-bleeped-<- (someone only after you for their own pleasure).
My point is, just be careful in that they aren't complimenting you for the wrong reasons.