hmm, I'd hazzard a guess replies like 'thanks for the info' that are out of context like that are proboably from xrumer or similar bots testing the water for spamming. they might do it so they have a postcount of 1, which on some forums may give them access to then make their own threads. (a common anti-spam permissions setup) so I would guess it was just another bot.
that's not spammer, however alot of time it is, even when they just have something like "thanks for the info", makesure you check the user profile, alot of times that's where the actual spam is...