No, they don't. In spite of the confusing wording in the post you cite, its petabytes/year claim is not derived from the 500m tweets/day claim – it must include metadata and/or multimedia.
This was all already derived (correctly) in the original post. Recapitulating:
500m tweets/day * (conservatively) 512B/tweet * 365 days/yr ~= 90 TiB/yr
Assuming compression and variable-length encoding of this long tail in colder storage, it's more likely <20 TiB/yr (<=115B/tweet on average)
Yes, this excludes analytics metadata, which as you suggest would not support Twitter's current ad products. But your core repeated claim about tweets alone is two orders of magnitude off.