I somewhat agree, but only to a point.

If you buy and sell a stock or other asset with an average hold time of hours, days, or weeks, yes, you are trading.

If your average holding period is months, you may be trading.

If your average holding period is years or decades, you're investing.

The thing is, if you buy an asset, you should have a reason to do so. As long as that reason remains valid, you keep holding the asset. However, sometimes that reason stops being valid, in which case you should sell. For example, say you buy a stock for its reliably high dividend, and the company slashes or cancels the dividend altogether. Should you keep holding it?

That sort of buying and selling is a valid way to invest.