Perhaps it’s slightly poorly drafted, but clearly it isn’t going to be an “LNER journey” when you’re travelling with a completely different operator. Presumably the majority of journeys booked through their website are on LNER services, so the standard boilerplate wording will reflect this.
Can you quote the specific text that you think is misleading?
As I said the email is entitled "
Sheff1, get ready for your journey with us" The journey is from Sheffield to St Pancras and the "us" is clearly LNER as the email is from them.
The body of the email reads:
"Hello
sheff1, We’re looking forward to welcoming you onboard between Sheffield and London St Pancras. Whether you’re off on an adventure, off to work, or visiting family or friends, we’ve got everything covered to make your trip with LNER as stress free as possible.
Your LNER Journey
Let's Eat at your seat. Order food and drinks directly to your seat! As a Perks member you get 10% off."
~~~
In another thread about false cancellations I mentioned receiving a text from LNER saying that the connecting train (operated by Northern) was cancelled. It wasn't and ran to time. Other people have reported receiving texts from LNER telling them to look for coach C & J on 2-coach Northern trains as they haven't booked a reserved seat (Northern don't reserve seats).
It would appear LNER have major issue in sending, at best, misleading 'updates' to people who have booked via them for other operators. Whilst I expect you are correct that most bookings are on LNER services, they have been actively promoting booking tickets for all operators via them using generous cashback offers - the very reason I use them for non-LNER journeys. Sending out standard wording which is, in fact, only accurate for their own services does not sound like a well thought out policy.