Pedagogical materials commonly advise adding a determiner or quantity word to "do [the/one's/some] Ving." However, in the following passage, "doing grocery shopping" does not have a determiner in it. Is it an error? If it's idiomatic, how do we reconcile such examples with pedagogical materials?

The man said he bought the Big Wednesday ticket to pass the time when his wife was shopping last week. His wife was doing grocery shopping again when he returned to the counter and found out he had become a multi-millionaire.

https://www.stuff.co.nz/editors-picks/10472963/You-ve-just-won-20-million

Pedagogical materials commonly advise adding a determiner or quantity word to "do [the/one's/some] Ving." However, in the following passage, "doing grocery shopping" does not have a determiner in it. Is it an error? If it's idiomatic, how do we reconcile such examples with pedagogical materials?

The man said he bought the Big Wednesday ticket to pass the time when his wife was shopping last week. His wife was doing grocery shopping again when he returned to the counter and found out he had become a multi-millionaire.

https://www.stuff.co.nz/editors-picks/10472963/You-ve-just-won-20-million

In Michael Swan's Practical English Usage, he offers the following examples:

Could you do the shopping for me?

I hate doing the ironing.

If these sentences cannot have "the" left out, why does the first quoted example not have a determiner?