They should really stress that low cost is limited to monetary cost only. It does not infer lower capability (at least this is what I'm assuming). In fact it has no real direct correlation to capability, as much as these two things are often and rightly associated.
J-10CE is much more inexpensive than many 4.5 gen fighters on the market. It can literally be called a "low cost alternative to Rafale/ Typhoon/ F-16V/ Gripen EF". It doesn't mean it can't clap those fighters in a fair fight.
Chinese people are often abysmal marketers and lack the awareness of finessed salesman language. Thinking far too literally here but they probably thought "alternative" already implies same level without knowing that "low cost" implies the opposite.