Also, you may wonder why you didn't know that McHenry was the designated Speaker Pro Tempore. It's because the list is kept secret by the clerk until a replacement is needed. So when they voted to get rid of McCarthy, no one (except McCarthy) knew who the temporary successor would be.
Also, even if the parliamentarian goes with the restrictive interpretation of McHenry's powers (where he can only preside over speaker elections), the House still has an option it didn't have in January: they can elect a temporary speaker, who becomes an "elected speaker pro tempore", a position which has specific (broader) authorities. Then they can take their time electing a permanent speaker and conduct whatever other business they want first.