Yes. Very much so.
OP it sounds like your supplier bought gelatin capsules and filled them himself. This is very common for UGLs to do with all oral drugs. There is no way to know what you have in the capsules. Theres no point to discuss this in depth because as I said, you have no idea what's in there, BUT the volume of powder is irrelevant.
The amount of active ingredient is tiny. To measure the stuff accurately a UGL will mix the activie ingredient with maltodextrin or flour or some other powder with similar grain size (so they mix evenly blah blah). So whether theres 100mg of product or .25mg of product is not dependant on how much powder is in the capsule.
I do not recommend research chemicals these days. Too many shady operations. Drop the cash on pharm grade arimidex if you want a guarentee that youre getting anastrazole.