There are additional reasons why I agree with that.

When the BTC/USD was declining, holding on to your bitcoins meant the buying power (in terms of USD) was becoming less over time. (i.e., we had "price inflation").   So selling bitcoins as soon as they were earned provided the greatest results (again, in terms of USD).

Now the opposite is happening, and thus the longer one holds onto bitcoins the greater the spending power from those coins.

There is another factor at play as well, though I only have anecdotal evidence of it occuring:
New miners appear to generally sell much of their mining output earned until their breakeven point is reached (i.e., until total revenue matches the amount invested.)  But after breakeven has been reached the bitcoin proceeds earned are kept for investment.  Many of those new miners resulting from the February boost have either recently just reached breakeven or they will be hitting that point very shortly.

Thus as the price rise results in breakeven being reached faster for many, the number of bitcoins these miners are supplying to the market decreases faster as the result.

Of course both of these contribute to and are vulnerable to cycles where found are peaks needing correction and troughs that offer a buying opportunity.

[edited]