When the alternative is your entire nation have ZERO vital infrastructure in that category? Yeah it IS an excuse for nationalization. We ALMOST did the same when the Japanese wanted to buy US Steel, but eventually came to an agreement about partial nationalization where it'd remain a private entity, but with the federal government as a shareholder with a "golden share" which is a concept in business used by governments to be able veto and override ANY decision made by said business' leadership if they deem it to be not within national interests. The difference is that Nippon wanted to actively expand US Steel's operations, whereas the chinese wanted to shutdown the British steel company an shutter all their plants, thus taking away the entire countries ability to produce primary steel (IE from raw iron instead of recycled scrap)

You can't have an absolutist view point for things like national infrastructure. It should have never landed in Chinese hands in the first place without something in place like what we did with US Steel, so that's on them, but because it DID, them nationalizing it instead of letting it be shutdown is the only real option, or else it would be a national emergency. You HAVE to have things like oil/gas, primary steel production, cement, lumber, etc. Those're the basic ingredients for modern society, and if there IS no private entity in your nation willing to do it anymore, your only choice IS nationalization.

Don't get me wrong, its the UK's fault they're even in this position since all of their retarded emissions laws have made things like Steel mills VERY unprofitable in recent decades because all of their profits get eaten up in emissions compliance bull crap. So I don't feel too much sympathy, but even THEY realize you can't have literally ZERO primary production capacity as a nation or else you'd start falling into collapse, so when the two choices are, nationalize the chinese owned asset (who, to be quite frank, I don't care about either, I think all chinese assets in the US should be seized and resold on the market myself) or LOSE one of your national strategic assets permanently, the choice to nationalize is obvious.

You could argue this is some cabal-ish long game, and I wouldn't be surprised, but its equally likely its just sheer incompetence and stupidity since its ONLY primary production affected by all of this, and not secondary production (making steel out of scrap steel) which is only SLIGHTLY better emissions wise but cheaper to actually do since scrap steel is cheaper than raw iron and coal and easier to work with in an ARC furnace than a blast furnace.