Threatened with legal action (defamation) over a negative but honest google review

Location: Ontario
To make a long story short, I had a bad experience with the boss of my new job before being let go. I left a negative but truthful review about my experience, then received an email from my ex boss for a cease and desist due to defamation. I only included things that are factual and excluded any of the emotional stuff, and I feel like the threat is just to scare me as it wasn’t written or sent by a lawyer, but I’m still afraid a bit.