Ubuntu – tar.xz extracting error “xz: (stdin): File format not recognized”

I am trying to extract a .tar.xz file on my Ubuntu Mate computer. No matter what I do, I get this error:

xz: (stdin): File format not recognized
tar: Child returned status 1
tar: Error is not recoverable: exiting now

I have done the following (although my repeated attempts to circumvent the error may highlight my ignorance):

tar xf file.tar.xz

Then,

unxz file.tar.xz #results in file.tar

That time, I got this similar error:

unxz: file.tar.xz: File format not recognized

Then, I did this:

tar -xJf file.tar.xz

Etcetera…

I tried updating/installing tar and xz-utils using

sudo apt-get install xz-utils

for x-utils, and

sudo apt-get install tar

for tar. They both updated/installed successfully, but when I did the above things again, I got the same errors.

EDIT ONE

When I use:

file file.tar.xz

I get

file.tar.xz: HTML document, UTF-8 Unicode text, with very long lines

When I try to open it with Engrampa using

engrampa file.tar.xz

I get the same error mentioned above.

I am running Ubuntu Mate 16.04 on the Raspberry Pi 3.

The output of

apt list xz-utils

is

Listing... Done
xz-utils/xenial,now 5.1.1alpha+20120614-2ubuntu2 armhf [installed]

The output of

xz --version

is

xz (XZ Utils) 5.1.0alpha
liblzma 5.1.0alpha

The output of

tar --version

is

tar (GNU tar) 1.28
Copyright (C) 2014 Free Software Foundation, Inc.
Liscense GPLv3+: GNU GPL version 3 or later <http://gnu.org/lisenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by John Gilmore and Jay Fenlason.

I obtained the file (pepper-flash-v.20.0.0.228r1.tar.xz) by using the command line

wget http://dl.free.fr/qVkzvqSiB -O pepper-flash-v20.0.0.228-r1.tar.xz

EDIT TWO

Thanks for all your answers. This question is closed.