I have also been curious about how the popular dating app got it's unusual name.
According to the Milwaukee Business journal, the founder, Jonathon Badeen explained they originally thought of the name Matchbox. However, this was rejected and Tinder was chosen as it continues with the fire theme.
Also Tinder sounds similar to Tender which has romantic overtones.
More information can be found here http://www.bizjournals.com/milwaukee/print-edition/2014/03/28/all-in-a-name-why-is-it-called-tinder.html