Algorithmic trading here means more about how to "execute trades" thus reduce the "execution cost" of a trade, rather than using quantitative method to gain advantage (alpha). They are usually employed by firms executing large trades, no mather whether the trade comes from a traditional trading form, or a quantitative trading firm. There are definitely overlaps, especially for HFTs regarding market microstructure, but in HTFs case, the market microstructure is built-in the HFT strategy itself, while for algorithmic trading can be decoupled as execution from the actual trading strategy that produces the majority of the "alpha"s.