Although the seed leaves of many plants are different to the mature leaves, the pepper leaves should be recognisable. I've grown cayenne peppers from the seed from dried peppers many times. The plants are very similar to capsicums or sweet peppers but just a bit smaller and slower to develop.
I suspect that if the leaves are very different on yours, that a weed seedling or something else has developed in the compost or has flown in from somewhere.
One way of avoiding this with many seed is to sow into vermiculite or perlite in a small tub, cover with plastic and prick on the seedling as soon as two seed leaves are open. That way you are less likely to have stray seeds coming up with things of which you are unsure. Pepper seeds prefer temperatures of at least 80F to germinate and germination can take two or three weeks.
It's not too late to resow if you don't mind waiting until well into autumn for your cayenne peppers.