As someone previously pointed out, there's a decent chance the entry and seizure were not voluntary. Some cops are just bad people. Once a victim of LE 'creative report writing', I am skeptical of any claims made by LE.
Scenario 1 - cop seizes firearm, lies in his report that owner "voluntarily requested" him to do so.
Scenario 2 - cop tells drunk gun owner, "either you sign this consent form or I arrest you and seize your gun anyhow." (Drunk gun owner signs off, knowing nobody would believe him over a LEO even if he were sober.)
Scenario 3 - Drunk gun owner gave consent and all is on the up-and-up.
We'll probably never know.