Your supposed to be a viking, there are no rules

It depends on your Kingdom.  There are many kingdoms where people attack troops on tiles either generally or the troops of those they regard as enemies.  But there are a few kingdoms where it is expressly or tacitly agreed that no one will attack the troops on tiles where the troops are from that kingdom.  Troops from other kingdoms are always fair game.

Perhaps your Kingdom is one where a no tile hitting rule holds sway.  If so you are fortunate.  Such Kingdoms tend to do very well and often enough find other ways to combine together for the general good.  Regularly winning KvK, KvKr and Fury events confers valuable bonuses; and the ability to yield tier 7, 8 and 9 tiles safely is another very considerable boon.

What I suggest - assuming the language barrier to be a problem - is to reply apologising and saying it was a mistake (if you have someone who speaks Imogi that will help) then watch for a while and you should be able to see if a no tile hitting agreement is in place.  If all the tiles in the forest are constatly being yielded that alone is a sure sign.  And in that case: 1.  don't tile hit; and 2.  seek a way to open comunications with the Russian clans.

As John wrote, a lot depends on the kingdom, how new it is, and who thinks they should be in charge, also, some players have very thin skins and take affront at the least thing, even when there is no provocation.

First, did you know that the tile was occupied when you sent your march?

In order for there to be a battle on a tile , at least one of the parties has to have no sheld. 

If you dropped your shield to attack, its a different matter to not having a shield sending to a tile an arriving ther after  someone else. either because they were nearer,move faster,or purposefully sped up to beat you there.

Though it does happen, some players can take offense if you go to a lair after they have killed the invader/despatched the ghost.