I did some validation, and the filtering logic used in the notebook seems consistent with the output we have for the 2021-01 and 2021-02 runs on the whole set of languages. I could not find any "page redirect" instance in data.

Redirect pages are a special filtering case. By default categories are filtered based on their wikidata instance of qid. Redirects however are excluded by selecting pages where mediawiki_page.page_is_redirect is false in wikipedia dumps.
The page_is_redirect column doc tells us that a value of 1 here indicates the article is a redirect; it is 0 in all other cases.

The query below shows that no articles with page_is_redirect=1 are present in the model output

select snapshot, mp.page_is_redirect, count(*) as articles from imagerec im
join wmf_raw.mediawiki_page as mp
where im.wiki_db = mp.wiki_db
and cast(im.page_id as string) = cast(mp.page_id as string)
and im.snapshot = mp.snapshot
and im.wiki_db != '' and im.snapshot >= '2021-01'
group by im.snapshot, mp.page_is_redirect

Results in

As an additional validation step, I found no instance of "page redirect" wikidata items (e.g. https://www.wikidata.org/wiki/Q21528878) present in the data.
For example, a crude grep through the raw output returns no match for Q21528878. The query

select instance_of, count(*) from imagerec_parquet where wiki_db != '' and snapshot = '2021-02' and instance_of like '%21528878%'  group by instance_of;

Returns no entry.