Chrome Accessibility Dev Tools seems to be looking for an exact match of '700' or 'bold' to be counted as bold. @alice I think there is a bug here. I'll try to remember to log it on Monday - but setting font-weight of 800 (which should be bold) doesn't return bold in the dev tools I think.
From James Nurthen:
https://github.com/GoogleChrome/accessibility-developer-tools/blob/b5fd54a6629125b582d10f7b183c7a23151d0894/src/js/AccessibilityUtils.js#L282