A German train company claimed Greta Thunberg travelled in first class after the climate activist posted a picture of herself sat on the carriage floor with bags and suitcases.
The 16-year-old published the photo on Twitter on Saturday with the caption: "Traveling on overcrowded trains through Germany. And I'm finally on my way home!"
Deutsche Bahn replied apologising for the inconvenience and saying they would “continue working hard on getting more trains, connections and seats".
However, they later deleted the tweet and seemingly changed their tone.
The company tweeted: "Dear Greta, thanks for supporting us railroad workers in the fight against climate change.
"We were pleased that you were on the ICE 74 with us on Saturday.
"And with 100 per cent green electricity.
"It would have been nicer if you had also reported how friendly and competently you were looked after by our team at your seat in first class."
The train company later confirmed the climate activist had travelled first class between the cities of Kassel and Hamburg.
Greta said she had only been able to get a seat after Göttingen, more than four hours into her journey, before having to change in Hamburg for a further train to Sweden.
Greta replied: "Our train from Basel was taken out of traffic.
"So we sat on the floor on 2 different trains. After Göttingen I got a seat.
"This is no problem of course and I never said it was.
"Overcrowded trains is a great sign because it means the demand for train travel is high!"
Greta travelled by train from the COP25 UN climate conference in Madrid and stopped in Turin, Italy, for a climate protest on Friday.
The teenager apologised for saying world leaders should be "put against the wall" while addressing a Fridays For Future protest in the Italian city.
In English, the expression is associated with execution by firing squad, but Greta said it has a different meaning in Swedish, her native language.
"Yesterday I said we must hold our leaders accountable and unfortunately said 'put them against the wall'," she said.
"That's Swenglish: 'att ställa någon mot väggen' (to put someone against the wall) means to hold someone accountable.
"That's what happens when you improvise speeches in a second language.
"Of course I apologise if anyone misunderstood this.
"I cannot enough express the fact that I - as well as the entire school strike movement - are against any possible form of violence.
"It goes without saying but I say it anyway."
The climate activist, who does not travel by plane because it is considered harmful to the environment, is now on her way back home to celebrate Christmas with her family in Stockholm.
Last week, Greta was named the Time magazine's Person of the Year for her actions in fighting climate change.
