Undisclosed aggressive behavior?

I was booked for a housesit, did the meet and greet, all three dogs were absolutely wonderful. I was told the senior dog may have food aggression tendencies just because they are older and a recent rescue, but the two other dogs are absolutely fine and content.

Fast forward to today - I have already spent my first night there and had zero issues, but when preparing to leave for work (which the owners were aware about), the easy going dog got suddenly aggressive and lightly lunged at me when I moved my workbag to their table. I was incredibly confused and called the owners, asking if this behavior was normal, one of them said normally they are easygoing but they were aware there might be some aggression sometimes. Their main owner let me know that this is in fact normal behavior and the act of leaving the house ends up in the dog being aggressive, and that they usually calm down and are fine when they get back.

The problem is, I am set to housesit for the next 4 days, and I'm a little worried about escalation. They said keys jingling might set the dog off, or putting on any sort of shoes, and I have picked up that moving around bags, or any large items like laptops also set them off. I'm going to attempt to go back in, but I was thrown off by the fact that I wasn't told about this behavior - I would have had a better plan lol.

I believe it is separation anxiety since I spoke to their other sitter and they said that they have acted that way with them as well, have any of you guys had a situation like this? How did you handle it? The dog is very food driven so I might attempt to get some of the calming treats I use for my own dog and see how those work, but I'm a little shaken up by the lunge (dog has some big chompers on them).