While the word "bug" is legit term for a whole family of insects, its also used commonly for basically all - and mainly unwanted - insects in general.

And I think that the lax common usage of the word "bug" is the result of the fact that the big majority of people neither know nor care about the differences between various insect taxa - and if they are the same anyway, it doesn't matter whether to call them bugs, beetles or whatever.
It may be right that many English speaking people are using the word "bug" for all insects, but neverthelss, you will always find "beetle" connected with the scientific term "Coleoptera" and "bug" with "Heteroptera" in specialist books.

Apart from that, whenever possible I prefer the usage of the scientific names (here: "Coleoptera" and "Heteroptera") of the various taxa because they are more accurate and unambiguous. However, when writing here I have to make some compromises so that every reader can understand what I mean.

Finally, my painful experience (in general but also every single day here in "Fascinating Insects") tells me that confusing bugs with beetles is far from being a linguistic problem only. Most people simply don't know the differences between the various insect taxa, which means that an article like this one is really urgently needed.