I think AMD and NVIDIA's
affiliation with gamers and avoidance of crypto miners (which seem to make up a surprisingly significant amount of their sales), is going to give BITMAIN quite a significant advantage when they release their E3 miner and other altcoin ASICs.
The recent fall in price will probably decrease AMD and NVIDIA's crypto-related sales, which could also decrease their focus on producing specialised hardware for miners.
If they don't focus on it now and BITMAIN enters the space quickly enough, they might be too late to preserve their share of the market. BITMAIN could be a serious threat to their recently increasing stock prices.
of course they are going to say they are focusing on gaming but they obviously know that they are in fact creating new hardware for altcoin miners. and that is why the article is saying they are worried!
and i think it is a good thing, they are feeling the competition and Bitmain will also have to compete with them. and in the end we may even start seeing Nvidia and AMD ASIC miners by these companies and all these competition can make everything better for us.