[Foobar]

  Well at least now you know what you are dealing with.  The down side is, HB is much easier to get rid of than knotweed .

[YorkshireLass]

Call it a brain fart and sidle away quietly 

[Penninehillbilly]

LOL
At least you're brave and honest enough to admit it arobwk,
Bad shock for your friend, but worried about contractor plant knowledge 
I hope you made sure no bits went home with you, scary thought having that stuff around.
Back in the 70s there was a patch where I walked the goats for grazing, used to walk in among it, never thinking what a problem it would turn out to be.

[Foobar]

I have two clumps of JKW I'm battling with (there is loads around this area).  It has just started shooting so it will be interesting to see what it does this year compared to last, as it had several chemical treatments last year.  Fingers crossed it will be less vigorous!

[big soft moose]

incidentally pulling JKW is mostly a waste of time - if you arent organic inject each stem with round up  - if you are hack it down and have a nice hot fire on top of it , or blaze it with a propane torch

[arobwk]

To be as fair as I can be to my friend, he was more into grass keeping once upon!  But he has firmly asserted, in most recent discussion,  "I have seen the pink flowers myself".  So perhaps (as you say Scarlet.D) there is a mix of the weeds - but I really doubt that.
Must go search "pink-flowered knotweed"!
Whatever, it has been agreed that he will leave a small 'stand' of weed to reach early flowering stage for re-evaluation/final identification later this year.  I can't wait (although I suspect the real culprit will be identifiable a bit before then).  We shall see.

[Foobar]

We had two hard frosts last week ... and to my absolute glee it's knocked all my knotweed down to the ground!  hahahaha!

I know it'll be back but it's just nice when you see the enemy limp and droopy just because a bit of cold