The question was not if Bitcoin overall is deflationary. The comment said it was by design, which it arguably isn't because by design it's actually inflationary.
Once all bitcoin is issued, there will never be any more. That is intrinsically deflationary.
I really don't see how you can argue that bitcoin is inflationary by design when the period of inflation is a temporary necessity for the initial issuance, and then never repeats[1].
The new coin supply (block subsidy) is reducing at an exponential rate and will soon not be able to even compensate for the rate of lost coins.