documentclass[final,a4paper,notitlepage,10pt]{report}

usepackage[utf8]{inputenc} % inputenc for encoding to utf8

setlengthparindent{0pt}

begin{document}
thispagestyle{empty}   % this page does not have a header

Testing some text on the first line.\
begin{tabular}{l l}\
Lorem ipsum & dolor sit amet
end{tabular}\
Why was the table above indented? and how can I reduce the space between first line and start of the table?

end{document}

documentclass[final,a4paper,notitlepage,10pt]{report}
usepackage[showframe]{geometry}
usepackage[utf8]{inputenc} % inputenc for encoding to utf8

setlengthparindent{0pt}

begin{document}
thispagestyle{empty}   % this page does not have a header

Testing some text on the first line.

vspace*{-baselineskip}
begin{tabular}{@{}l l}\
Lorem ipsum & dolor sit amet
end{tabular}\
Why was the table above indented? and how can I reduce the space between first line and start of the table?
end{document}