Yep, that's exactly it. If you use a Thermal against him, yer screwed.
Say, now that you mention it, as I recall, you CAN'T get a Thermal Detonator with Qui-Gon. Thermal Detonators in large populated areas, like Mos Espa and the Arena, were inherently BAD IDEAS, and I thought we made it so that there were no Thermals available on Tatooine. I could be wrong, but I'm pretty sure that we put no TDs there.
If that's the case, then were you, perchance, using the IAMOBI cheat?
Ah - although, you COULD have gotten a set of 5 Flash Grenades on Tatooine. You might have thrown one up near Jabba, which might kill some of Jabba's entourage, which would get the whole place angry at you.