Work laptop password mysteriously sent via iMessage - need advice

I have a work MacBook with a monthly password change policy. Today I discovered that my current laptop password was sent via iMessage to a family member - but I never sent this message.

Key details:

• My personal iCloud is logged into the work laptop (for iMessage only)
• I haven't shared the password with anyone (not even with the IT dept, which takes out of question a possible data breach at the company)
• The message only appeared on my phone, not the laptop
• Both devices have been in my physical proximity, so there is no question of someone physically accessing it. I also do not think I used the work laptop on my public network WiFi.

I've have this incident changed both my Apple ID and laptop passwords.

Has anyone experienced something similar? What should I investigate or do next?