Bacillus thuringiensis Israelenses (Bt -I) is used to control the larvae of certain members of the Diptera order, including mosquitoes and many different kinds of gnats.

Bt-Kurstaki (Bt-K) is the strain used for the caterpillars of moths and butterflies. I very strongly suspect that the product you saw was Btk, not Bti.

Bti is the active ingredient found in mosquito dunks (look for them in the big box stores), or Gnatrol.

Thanks.
On second look it is indeed BTK