Would a loud backfire through the intake manifold while cranking engine on 93 grand am sohc mean that you just ruined a valve cause it started yesterday with no problem and today this happened?

Yes...all valves bent...smacked piston...good old interference engines. Started cranking really fast cause valves stuck open from overheat then...BAM...backfire out intake after only 15seconds of cranking...Head back off again. answering own question. Impossible to say. You need to find out why it backfired. Suggest you do a compression test.