I was injured in an attack and off work for 6 months due to injury. I was released from my job, causing my HDHP to expire. Is this a coverage lapse due to disability?

It depends on your injury.

The IRS says:

Disabled

An individual is generally considered disabled if the individual is unable to engage in any substantial gainful activity due to a physical or mental impairment that can be expected to result in death or to continue indefinitely.

See Form 8889 Instructions.

If your injury disabled you and this led directly to the loss of the HDHP coverage, then I would say that the answer to your question is "yes". But you need to be able to defend this to the IRS, if they ever ask. That means document what you have now, because it is always harder to go back and do this years later when the IRS gets around to noticing.