"Armed with a knife or other sharp object." Ummmm Let's see, what was he doing when they arrived? Oh, yes, grilling. Could that by any chance mean he was carrying around a steak knife and fork to turn the meat and cut it? Nope, not sure that anyone grilling would have knife and sharp object in hand, would they?
How about this: Attemp to contact. Contact fails. Go back to office and document, make one of those lovely reports that the powers to be loves to have SW's and policemen do. Then, contact the family member(s) who made request of evaluation and explain what happened. Family member(s) will confirm that he always has a knife and sharp object in hand while grilling (after all, he does have his normal moments just like everyone else) and family will help with another contact attempt. Next time, family member visits first or is with the SW and police to help with the introduction of what is happening.