You ignored the second sentence of what I am quoting. Here it is again:

    The slightest force including pushing open a door is all that is necessary. 

Not my words. That said, force does not imply amplitude of said force, except colloquially. This is legal stuff though, which, like say physics, has slightly different use of certain words than most people are used to from day to day life.

As in, I would agree with you that force in regular use is usually used in the sense of a large force. But that is not the actual definition and o ly possible use of the word.