Worst anxiety came true!

Our 4.5 month old Jack Russell urinated on the bed. Since day one, I've been telling my husband I do not agree with the dog sleeping in the bed yet. I insist he sleep in his crate every night until it's been 3 solid weeks with NO accidents in the house. We've had the dog for 2 months and he's never gone to the bathroom on the bed. He's peed next to it. My husband swore up and down he'd never do it. It'd been about a week since his last "Accident in the house". Last night we were getting ready for bed. The dog ran under the bed (not too out of the ordinary), but would not come out when called. I sat on the bed and felt a wetspot . He peed on our bed when we weren't looking and my husband had just taken him for a walk.

What is this behavior possibly meaning?

I now know I am very justified in not letting the dog sleep in the bed. This helped me win the argument!!!

FYI: I'm not a dog person and my husband is and always has been.